1. Field of the Invention
The present invention relates to a device for detecting inclination of a boring head of a boring tool which is used to install pipelines under the ground without digging a trench.
2. Description of the Prior Art
When the ground is bored by a boring tool to install pipelines under the ground without digging a trench, it requires to grasp both horizontal and vertical positions of a boring head during the boring operation so as to correct the deviation relative to a planned course.
U.S. Pat. No. 5,165,490 in the name of the same assignee of the present application has proposed a device for detecting an angular position in a circumferential direction of a boring head having a slant surface as a reference surface. With the device of this U.S. patent, a magnetic field is intermittently generated from the boring head when the slant surface is positioned out of a predetermined angular range, while the magnet field is continuously generated when the slant surface is positioned within the predetermined angular range. Such a magnetic field is received by a receiver on the ground, and the receiver displays as to whether the inclination of the boring head in the circumferential direction is proper or improper. If the receiver displays that the inclination is improper, the boring head is rotated to correct the position of the slant surface so as to coincide with a reference angle, and a further correction is performed to correct the direction so as to correspond to a planned course.
With this prior art detecting device, however, although it can be operated to detect as to whether the inclination in the circumferential direction of the boring head is within the proper range, it cannot be operated to detect the inclination itself or an exact inclination angle in a rolling direction. Further, the prior art device cannot be operated to detect the inclination angle in an axial direction of the boring head or an inclination angle in a pitch direction. Therefore, the device is not operable to reliably correct the inclination according to the planned course, and it requires troublesome operation for such a correction.